The invention relates to an axial setting device comprising two discs which are rotatable relative to one another, and which are supported coaxially relative to one another in a housing. Between the two discs, there are guided balls in pairs of ball grooves whose depth varies across the circumference. One of the discs is axially supported and the other one of the discs is axially displaceable against elastic returning forces of a first spring. One of the discs can be rotatingly driven by a motor via a gear drive, whereas the other one of the discs is supported in the housing with respect to rotation.
In the disclosed embodiment, the rotatingly driven disc can also be the axially displaceable disc, whereas the disc held with respect to rotation can, at the same time, be directly axially supported in the housing. Alternatively, the axially supported disc can be rotatingly driven, and the axially displaceable disc which, in turn, is supported on same via the balls, can be held with respect to rotation.
For actuating the axial setting device, the motor is driven in a first direction of rotation, wherein the one of the discs connected to the motor via reduction stages is rotated, with the balls rolling by half the angle of rotation of the driven disc on the disc held with respect to rotation. The axially displaceable disc, in turn, supported via the balls on the disc axially supported in the housing, is axially displaced against elastic returning forces of the first spring.
The balls resting in a starting position against end stops in the pairs of ball grooves, which balls, at the same time, are positioned in the deepest groove portions, as a result of the relative rotation of the discs relative to one another, move by approximately half the angle of rotation towards flatter groove portions. As a result, the discs push away from one another and reach an operating region in which they can apply axial setting forces.
If, starting from the operating region of the discs, the motor is de-energized, the elastic returning forces of the first spring as applied to the axially displaceable disc cause the latter to be pushed back. The at least one rotatingly drivable disc is rotated back due to the effect of the balls in the ball grooves, until the balls in their pairs of ball grooves simultaneously stop against the end stops. Substantially the same happens if, starting from the operating region of the discs, the motor is driven in the opposite direction until the discs again reach the starting position, and until the balls in their pairs of ball grooves simultaneously stop against the end stops. As a result of the balls stopping against the ends of the ball grooves, the rotating masses of the system, i.e. the rotatable one of the discs, the gears of the gear drive and the shaft of the motor together with the rotor mass, are stopped abruptly.
The impact generated by the abrupt stopping of the rotating masses can lead to tooth rupture at the motor pinion or at the gear set, or to other mechanical damage. Accordingly, there exists a need for an improved stopping mechanism which accommodates impacts generated during braking of the rotating masses.